Dynamic Properties of Wood Obtained by Frequency Resonance Technique and Dynamic Mechanical Analysis

Abstract

The study of the visco-elastic properties of wood involves the determination of dynamic parameters using non-destructive methods. These methods differ in the possibilities of use (size and geometry of tested specimens, control of environmental conditions such as temperature or humidity), in the field of use (laboratory only, in-situ), and also in the way of determining dynamic parameters. This brings the question of whether the same parameters determined in different ways can be considered identical. This study aims to compare the Frequency Resonance Technique (FRT) and Dynamic Mechanical Analysis (DMA) as methods used for the determination of bending dynamic modulus of elasticity (MOED) and damping coefficient (tan δ) of dry and green wood. Groups of specimens of European beech (Fagus sylvatica L.), Small-leaved linden (Tilia cordata Mill.), European oak (Quercus robur L.), and Norway spruce (Picea abies L.) wood with three levels of moisture contents (MC) were tested with both methods. Obtained results showed that MOED decreases with increasing moisture content until the fibre saturation point (FSP). Above FSP, there is not any significant change in dynamic modulus with increasing MC. A strong linear correlation between MOED obtained through both methods was found (r = 0.92, r² = 0.84). For tan δ, the relationship was weaker (r = 0.57, r² = 0.32), and each method shows a different influence of MC on damping tan δ above the FSP, which leads to resume that this damping coefficient is sensitive to the method of determination.